Dtmf Controlled.ppt

We Are Going To Discuss • What is DTMF? • How to control a robot using DTMF? • DTMF Keypad table • HT9170B IC

• Application Circuit • Sample Code

DTMF (Dual-Tone-Multiple-Frequency) • DTMF signaling is used for telecom signaling over analog telephone lines in the voice frequency band between telephone handsets and other communication devices and the switching centre. • In other words DTMF is a method of instructing switching system of the telephone numbers to be dialed, or to issue commands to switching systems.

DTMF Keypad Table

Table Description • • • •

DTMF table is laid out in 4*4 matrix. Row represents low frequency . Column represents high frequency. The multiple tones are the reason for calling the system multi frequency. • Tones are then decoded by switching centers to determine which keys are pressed.

DTMF Decoder/Receiver IC (HT9170B)

• Operating voltage : 2.5V – 5.5V • Minimal external components • No external filter required • Excellent performance

• 3.58 crystal or ceramic resonator • 18 pin package

Application Circuit

Working Of The IC • Tone is attached to 0.1 micro F capacitor on the top corner. • Mount the circuit on the robot with auto answer mode on. • Connect one wire of the headphone to the wire and other to the ground. • The tone is then passed to amplifier for filtering.

• OE is the output enable pin, high on this pin will enable the output . • D0,D1,D2 and D3 are the decoded output of the IC.

Working Of The IC • DV is data valid pin, it’s a output pin, Set to high itself by IC when valid data is available on these bits. • RT/GT and EST are pins for setting effective time duration of tone to check for authenticity.

Connecting Cell Phone To Circuit • Connect the cell phone to circuit.

• Call the cell phone from a remote phone • Now press the keys on the remote phone and you will see the LED’s blinking.

Interfacing HT9170B With ATMega8 • Connect d0,d1,d2,d3 to Port C0,C1,C2,C3.

• Now we can check respective bits with programming and respond based on the bit pattern received. • Now based on the input pattern we can instruct the motor with specific commands and make the robot move in different directions.

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